This invention relates in general to sewing machines and in particular to a new and useful sewing machine having a needle holder magazine.
A prior art thread changing mechanism disclosed in German OS No. 29 27 142 and developed for a small embroidering machine with a plurality of needle bars, provides for each needle bar a magazine which is dsiplaceable transversely to the longitudinal axis of the needle bar and accommodates a plurality of needle holders, each carrying a needle, of which one at a time can be coupled by non-positive coupling means to the needle bar. For changing the thread, the embroidering machine is stopped and the needle bar is lifted above the top dead center of its working stroke to execute a switching stroke by which the needle holder connected to the needle bar is retracted to the magazine and simultaneously uncoupled from the needle bar. As soon as the needle bar at the end of the switching stroke is completely withdrawn from the magazine, the needle holder needed for the next embroidering operation is brought into a standby position by displacing the magazine, whereupon the needle bar is lowered again and the new needle holder is coupled to the needle bar.
In a development of a thread changing mechanism which was accomplished in practice yet not published in print, the non-positive coupling means have been replaced by positive ones. These means comprise stepped inner guide or coupling surfaces of the needle holder, which extend parallel to the direction of displacement of the magazine. At the end of the needle bar, corresponding outer guide or coupling surfaces are provided. To change the thread, again a switching stroke is necessary, above the top dead center of the working stroke. Then, the magazine is displaced, whereby the coupled needle holder is displaced by the next needle holder of the magazine sidewards, away from the needle bar and thus uncoupled and introduced into the magazine. The adjacent needle holder effecting the uncoupling thus automatically arrives at the coupling position.
This successive uncoupling and coupling of the row of needle holders takes place until the desired needle holder is connected to the needle bar. Then, the needle bar is lowered again into the top dead center of the working stroke, which withdraws the needle holder from the magazine so that during the following embroidering operation, the needle holder does not come into contact with the magazine.
Since the working stroke is followed by a long switching stroke, the total stroke of the needle bar is relatively very large and requires correspondingly spaced-apart bearing points. Further, another drive is needed for the switching stroke, so that the entire support and drive of the needle bar becomes a bulky construction requiring a correspondingly voluminous housing. In an embroidering machine, this raises no problems, since the size of the housing may easily be adapted to the space occupied by the mechanism. Considerable difficulties would be encountered, however, with an application of such a construction to conventional sewing machines.